A customer has asked us to implement a feature in which there is a browser endpoint on keycloak. This URL can be told to link to a specific identity broker provider (Google, Facebook, etc.) and then the browser would be redirected back to the client. Pretty much what exists in the Account Service console, but without having to look at the Account Service. The reason for this is that they are doing integration with a specific social provider and don't want to have to go through the Account Service pages. Seems pretty reasonable and valid use case... I'm worried about a couple of things: * The design of it * The security implications. The implementation would be simple enough, it would just extract code from the accoutn service. The endpoint would take a "providerId" paramter that would be the idp linking to, a "clientId" for the client requesting the link, and a "redirect_uri" to redirect back to after the link is successful. Obviously the redirect_uri would be validated against the clientId. Now comes the interesting part, the security implications. Account linking in the Account Service is fine and dandy and doesn't have any security holes because we guarantee that the Account Service initiated the linking via a CSRF check. For this new Client-Requested-Linking feature, if we do nothing, and just model it as above, we cannot guarantee that the client initiated the linking request. What are the implications of this? This feature would be vulnerable to CSRF. A rogue website could initiate account linking to a specific configured provider. Is this bad? I don't know. We can guarantee that the redirect uri is valid. The browser would never get back to the rogue website. So what can we do to improve this? * We could do nothing and hope its ok that anybody can initiate a link. * We could add a consent screen like this: "Application 'clientId' is requesting that you link your user account to 'providerId'. Do you agree to this? You will be redirected to this provider if you click ok.". This of course relies on the user to actually read the page. Is this good enough? * My last thought would be OIDC specific. We could use the POST binding trick that SAML does to do a browser redirect via a POST call. THe POST would contain the access token the client has. We match this token up against the browser cookie to make sure its the same session. We also make sure that the access token has permission to request a link. There are 2 downsides to this approach a) This requires some code on the client side to obtain the access token and then to package it up into an HTML document so the POST binding trick can be done. b) This will only work for OIDC clients. SAML clients will be left in the dust, although I guess we could allow SAML to push a signed assertion back. Thoughts?